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Heavy Snow 12/20/2010. Mike Bardou and Mark Ratzer National Weather Service Chicago, IL. General Event Synopsis. Snow expected to begin Monday 12/20 late afternoon/early evening Accumulation expected Snow to transition to freezing drizzle Monday night. Radar. By the Numbers. ORD. MDW.

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heavy snow 12 20 2010

Heavy Snow 12/20/2010

Mike Bardou and Mark Ratzer

National Weather Service

Chicago, IL

general event synopsis
General Event Synopsis
  • Snow expected to begin Monday 12/20 late afternoon/early evening
  • Accumulation expected
  • Snow to transition to freezing drizzle Monday night
by the numbers
By the Numbers

ORD

MDW

Snow began 2205z

SNINCR 0051-0151z

0151-0251z

<= 2SM visibility 2304-0506z

<= 1SM visibility 0026-0324z

Lowest visibility ½SM

Total snow: 3.4 in

  • Snow began 2217z
  • SNINCR 0051-0151z

0151-0251z

  • <= 2SM visibility 2258-0538z
  • <= 1SM visibility 2351-0251z
  • Lowest visibility ¾SM
  • Total snow: 2.5 in
forecast timeline sunday afternoon evening
Forecast Timeline – Sunday Afternoon/Evening
  • Winter Weather Advisory issued 350 pm

- Midnight Mon-9 am Tue

- Snow begins Monday Evening

- 0.5-1.5” snow then freezing drizzle

  • Update 537 pm

- Snow begins late Monday afternoon

- 1-3” accumulation then freezing drizzle

tafs sunday evening
TAFs – Sunday Evening

ORD

MDW

KMDW 192330Z 2000/2024 26006KT P6SM SCT100 FM200300 VRB03KT P6SM SKC FM201100 14005KT P6SM SCT100 BKN250 FM201900 14008KT P6SM VCSH SCT030 BKN060 FM202200 13010KT 4SM -SN SCT010 BKN020 FM202330 13012KT 3SM -SN BKN010

KMDW 200520Z 2006/2106 VRB03KT P6SM SCT200 FM201100 14005KT P6SM SCT100 BKN250 FM201900 14008KT P6SM VCSH SCT030 BKN060 FM202200 13010KT 4SM -SN SCT010 OVC020 FM202330 13012KT 2SM -SN OVC010

KORD 192330Z 2000/2106 26006KT P6SM SCT100 FM200300 VRB03KT P6SM SKC FM201100 14005KT P6SM SCT100 BKN250 FM201900 14008KT P6SM VCSH SCT030 BKN060 FM202200 13010KT 4SM -SN SCT010 BKN020 FM202330 13012KT 3SM -SN BKN010 FM210300 16010KT 5SM -FZDZ BR OVC010

KORD 200520Z 2006/2112 VRB03KT P6SM SCT200 FM201100 14005KT P6SM SCT100 BKN250 FM201900 14008KT P6SM VCSH SCT030 BKN060 FM202200 13010KT 4SM -SN SCT010 OVC020 FM202330 13012KT 2SM -SN OVC010 FM211000 13012KT 5SM -FZDZ BR OVC008

forecast timeline monday morning
Forecast Timeline – Monday Morning
  • Winter Weather Advisory now from 4 pm

- Snow begins late afternoon

- 2-4” snow then freezing drizzle

  • Update 1058 am

- no change

tafs monday morning
TAFs – Monday Morning

ORD

MDW

KMDW 201141Z 2012/2112 VRB04KT P6SM SCT060 BKN090 FM201700 14008KT P6SM SCT030 BKN060 FM202100 14013KT 3SM -SN SCT009 OVC015 FM202200 14013KT 1SM -SN OVC009 FM210200 15013KT 4SM -SN FEW004 OVC008 FM210600 16013KT 4SM -FZDZ BR OVC005

KMDW 201624Z 2016/2112 15007KT P6SM BKN090 FM202100 14010KT 3SM -SN SCT030 OVC040 FM202200 13011KT 1 1/2SM -SN BR SCT009 OVC015 TEMPO 2023/2103 3/4SM -SN BR VV006 FM210400 14011KT 4SM -SN BR FEW005 OVC008 FM210800 15010KT 3SM -FZDZ BR OVC005

KORD 201141Z 2012/2118 VRB04KT P6SM SCT060 BKN090 FM201700 14008KT P6SM SCT030 BKN060 FM202100 14013KT 3SM -SN SCT009 OVC015 FM202200 14013KT 1SM -SN OVC009 FM210200 15013KT 4SM -SN FEW004 OVC008 FM210600 16013KT 4SM -FZDZ BR OVC005 FM211200 17011KT 5SM BR OVC005

KORD 201624Z 2016/2118 16007KT P6SM BKN090

FM202100 14010KT 3SM -SN SCT030 OVC040

FM202200 13011KT 1 1/2SM -SN BR SCT009 OVC015

TEMPO 2023/2103 3/4SM -SN BR VV006

FM210400 14011KT 4SM -SN BR FEW005 OVC008

FM210800 15010KT 3SM -FZDZ BR OVC005

FM211600 17011KT 5SM BR OVC005

TEMPO 2116/2118 3SM -DZ BR

forecast timeline monday afternoon
Forecast Timeline - Monday Afternoon
  • Winter Weather Advisory Update -544 pm

- Heavy Snow

- 3-6”; rates possibly exceeding 1”/hr

- “…bursts of heavy snow making it near impossible for road crews to keep up with snowfall rates.”

tafs monday afternoon
TAFs – Monday Afternoon

ORD

MDW

KMDW 201740Z 2018/2118 16007KT P6SM BKN090 FM202100 14010KT 3SM -SN SCT025 OVC040 FM202200 13011KT 1 1/2SM -SN BR SCT012 OVC025 TEMPO 2023/2103 3/4SM -SN BR VV006 FM210400 14011KT 4SM -SN BR FEW005 OVC008 FM210800 15010KT 3SM -FZDZ BR OVC005…

KMDW 202005Z 2020/2118 13010KT P6SM SCT040 BKN090 FM202200 13010KT 3SM -SN SCT025 OVC040 FM202300 12011KT 1 1/2SM -SN BR SCT012 OVC025 TEMPO 2100/2103 3/4SM -SN BR VV006 FM210400 12012KT 4SM -SN BR FEW005 OVC008 FM210800 14011KT 3SM -FZDZ BR OVC005…

KMDW 202157Z 2022/2118 13010KT 3SM -SN SCT025 OVC040 FM202330 12011KT 3/4SM -SN BR OVC012 TEMPO 2100/2103 1/2SM SN VV006 FM210400 12012KT 4SM -SN BR FEW005 OVC008 FM210800 14011KT 3SM -FZDZ BR OVC005…

KORD 201740Z 2018/2124 16007KT P6SM BKN090

FM202100 14010KT 3SM -SN SCT025 OVC040

FM202200 13011KT 1 1/2SM -SN BR SCT012 OVC025

TEMPO 2023/2103 3/4SM -SN BR VV006

FM210400 14011KT 4SM -SN BR FEW005 OVC008

FM210800 15010KT 3SM -FZDZ BR OVC005…

KORD 202005Z 2020/2124 13010KT P6SM SCT040 BKN090

FM202200 13010KT 3SM -SN SCT025 OVC040

FM202300 12011KT 1 1/2SM -SN BR SCT012 OVC025

TEMPO 2100/2103 3/4SM -SN BR VV006

FM210400 12012KT 4SM -SN BR FEW005 OVC008

FM210800 14011KT 3SM -FZDZ BR OVC005…

KORD 202157Z 2022/2124 13010KT 3SM -SN SCT025 OVC040

FM202330 12011KT 3/4SM -SN BR OVC012

TEMPO 2100/2103 1/2SM SN VV006

FM210400 12012KT 4SM -SN BR FEW005 OVC008

FM210800 14011KT 3SM -FZDZ BR OVC005…

tafs monday evening
TAFs – Monday Evening

ORD

MDW

KMDW 202331Z 2100/2124 11009KT 1SM -SN BR OVC015 FM210030 11009KT 3/4SM -SN BR OVC012 TEMPO 2101/2103 1/2SM SN VV006 FM210300 12010KT 4SM -SN BR FEW005 OVC008 FM210800 13007KT 3SM -FZDZ BR OVC005

KMDW 210032Z 2101/2124 11009KT 3/4SM -SN BR OVC008 TEMPO 2101/2103 1/2SM SN VV006 FM210300 12010KT 4SM -SN BR FEW005 OVC008 FM210800 13007KT 3SM -FZDZ BR OVC005

 KMDW 210102Z 2101/2124 11009KT 3/4SM -SN BR OVC006 TEMPO 2101/2103 1/2SM SN VV004 FM210300 12010KT 4SM -SN BR FEW005 OVC008 FM210800 13007KT 3SM -FZDZ BR OVC005

KMDW 210149Z 2102/2124 11009KT 1SM -SN BR OVC006 TEMPO 2102/2103 1/2SM SN VV004 FM210300 12010KT 4SM -SN BR FEW005 OVC008 FM210600 13007KT 3SM -FZDZ BR OVC005

KORD 202331Z 2100/2206 11008KT 1SM -SN BR OVC012

FM210030 11009KT 3/4SM -SN BR OVC010

TEMPO 2101/2103 1/2SM SN VV006

FM210300 12010KT 4SM -SN BR FEW005 OVC008

FM210800 13008KT 3SM -FZDZ BR OVC005

KORD 210103Z 2101/2206 11009KT 3/4SM -SN BR OVC006

TEMPO 2101/2103 1/2SM SN VV004

FM210300 12010KT 4SM -SN BR FEW005 OVC008

FM210800 13008KT 3SM -FZDZ BR OVC005

KORD 210149Z 2102/2206 11009KT 1SM -SN BR OVC006

TEMPO 2102/2103 1/2SM SN VV004

FM210300 12010KT 4SM -SN BR FEW005 OVC008

FM210600 13008KT 3SM -FZDZ BR OVC005

KORD 210252Z 2103/2206 12010KT 2SM -SN BR FEW005 OVC008

TEMPO 2103/2105 1SM -SN BR BKN005

FM210600 13008KT 3SM -FZDZ BR OVC005

what we learned
What We Learned
  • Reinforced importance of snowfall rate information
  • Visibility alone does not always convey enough about snowfall rate
  • Aviation Discussion should highlight snow intensity
  • Need for hourly snowfall rate forecast information
using the forecast
Using the Forecast
  • TAFs – every 2 hrs (M-F); watch trends
  • Forecast Discussions – every 2 hrs (M-F)
  • Experimental Precipitation Outlook
  • Headlines – Warnings/Advisories
  • www.weather.gov/zau
speculation
Speculation
  • Flake size may have contributed to “better” visibility during the heaviest snow
  • Small flakes = better visibility?
  • Small flakes = slippery snow = more frequent runway treatment?
things for the future
Things for the Future
  • Study relationships between visibility and snowfall rate
  • Study role of flake size
  • Examine impacts of different flake size
questions
Questions??

Scott Shelerud

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